Problem: When creating more than 10 location lists and adding items one by
one a previous location may be used. (Audrius Kažukauskas)
Solution: Clear the location list completely when adding the tenth one.
Problem: After forcing an operator to be characterwise it can still become
linewise when spanning whole lines.
Solution: Don't make the operator linewise when motion_force was set.
Problem: When setting 'undofile' while the file is already loaded but
unchanged, try reading the undo file. (Andy Wokula)
Solution: Compute a checksum of the text when 'undofile' is set. (Christian